McHenry County Department of Health - Environmental Health
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FAQ's about West Nile Virus

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Q: What is West Nile virus (WNV)?
A:  West Nile virus is a flavivirus transmitted by the bite of an infected mosquito. This virus can cause West Nile encephalitis which is an inflammation of the brain.

Q: How do people get West Nile virus?
A: The principle route of human infection with West Nile virus is through the bite of an infected mosquito.

Q: Can you get West Nile virus from another person?
A: Current research indicates that WNV can be transmitted through breast milk, from mother to fetus, through blood transfusion or human organ transplant.

Q: Are other animals infected with West Nile virus?
A: To date, the bird population appears to be the most susceptible to the effects of West Nile virus. WNV has been shown to infect many animals including horses, cats, dogs, bats, squirrels and rabbits.

Q: Where can I report dead birds?
A: The Health Department collects a limited number of birds annually to be tested for WNV. The primary birds that are tested are crows, blue jays & robins. View a complete list of eligible birds.

Q: What mosquitoes carry WNV?
A: In Illinois, the West Nile virus is primarily associated with Culex species of mosquitoes. Culex mosquitoes lay their eggs in stagnant ditches, old tires, clogged gutters, old tin cans and anything that will hold water, especially artificial containers.

Q: How many mosquitoes are infected with the virus?
A: In areas where mosquitoes have been found to carry the virus, 1% - 2% are infected with WNV. The most common mosquito found in Illinois is the inland floodwater mosquito, which is not believed to be a significant vector for West Nile virus.

Q: How is the virus transmitted?
A: Mosquitoes become infected with the virus when they feed on infected birds. These infected mosquitoes can then transmit West Nile virus to humans and other animals.

Q: If I am bitten by an infected mosquito, will I become ill?
A: Even if the mosquito is infected, less than 1% of the people who are bitten will get severely ill. Around 20% infected will experience flu-like symptoms. Approximately 80% of people infected with WNV will show no symptoms at all.

Q: What are the symptoms?
A: Most people exposed to the virus will show no symptoms or mild symptoms including fever, headache, body aches, skin rash and swollen lymph glands. Severe infections are marked by headache, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis and rarely death.

Q: When do symptoms occur?
A: Symptoms generally occur 3 to 14 days following the bite of an infected mosquito.

Q: What population is most at risk?
A: Anyone can get the virus, but people over 50 years old or individuals with weakened immune systems have the highest risk of developing severe illness.

Q: Is there a treatment or vaccine for West Nile encephalitis?
A: There is no specific therapy or vaccine for West Nile encephalitis. Contact your physician if you or a family member develops symptoms.

Q: Is there a test for West Nile virus?
A: West Nile virus can be confirmed through a blood sample or through cerebrospinal fluid.

Q: What is the role of the Health Department?
A: Public Education

  • Track cases of human illness
  • Collection/submittal of dead birds for analysis
  • Collection and analysis of Culex mosquitoes for WNV
  • Remediation of sites that promote mosquito breeding (i.e. dumps, discarded tires, abandoned pools) through Ordinance enforcement.

Q: Does the County have a mosquito abatement program?
A: The County does not have a mosquito abatement program. Check with your township, municipality or property owner’s association. The McHenry County Department of Health typically offers free larvicide to qualifying governmental agencies to treat catch basins, etc.

Q: What can residents do?
A: The first and best defense against mosquitoes/mosquito borne illness is to eliminate the places where they breed.

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